Bandgap Reference Voltage Generation at Low Supply
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Solution Overview
Problem
Integrated circuits, particularly system-on-chip (SoC) devices, face challenges in generating accurate reference voltages at low supply voltages, as existing bandgap reference circuits are not adequately suited for low voltage operations and often have multiple operating points, requiring additional control circuitry to function correctly.
Innovation Solution
A bandgap reference architecture utilizing two substrate PNP bipolar junction transistors with different bias currents and a closed-loop feedback mechanism to generate a temperature-compensated reference voltage, capable of operating over a wide range of supply voltages as low as 1.1V, using PMOS transistors and resistors to stabilize the emitter voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuits are used, then reference voltage can be generated, but they cannot operate accurately at low supply voltages (below 1.2V) and require multiple operating points with complex control circuitry
Solution Approach 1:
The patent changes the operating parameters of the bipolar transistors by biasing them at different current densities (first transistor at higher current density, second at lower current density), which enables the generation of delta VBE signal. This parameter change allows the circuit to generate accurate reference voltages at low supply voltages without requiring multiple operating points or complex control circuitry.
Solution Approach 2:
The reference voltage generation is segmented into distinct functional components: the first bipolar transistor generates VBE1, the second bipolar transistor generates VBE2, and their difference (delta VBE) is extracted and combined with a fraction of VBE1 through resistor dividers. This segmentation allows each component to operate independently at optimized current densities, simplifying the overall control circuitry.
2Use of energy by stationary object
If bandgap reference circuits are designed for low voltage operation, then power consumption is reduced, but maintaining accurate reference voltage becomes difficult without additional control circuitry
Solution Approach 1:
The patent employs closed-loop feedback where the generated reference voltage is fed back through resistor dividers to the bases of the bipolar transistors. This feedback mechanism automatically adjusts the operating points of the transistors to maintain accurate reference voltage generation, eliminating the need for external control circuitry while preserving low power consumption.
Solution Approach 2:
The bandgap reference circuit is designed to be self-regulating, where the interaction between the two bipolar transistors biased at different current densities and the resistor divider network automatically maintains the correct reference voltage. The circuit serves itself by using its own output to control its input, eliminating the need for external power management or control circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate temperature-compensated reference voltage generation at low supply voltages, reducing the complexity of startup circuits and ensuring a stable operating point, thus enhancing the operational reliability of SoC devices in power-saving modes.
Implementation Method 1
the base to emitter voltage of first transistor is higher than that of the second transistor, which generates a delta VBE (differential base-to-emitter voltage) signal
Implementation Method 2
A first voltage divider (e.g., resistor divider) generates a divided voltage of a VBE (fractional VBE) at a first center node
Data Source
AI summary
A bandgap reference voltage generator includes a first and a second bipolar junction transistor, which is biased at a lower current per unit emitter area than that of the first transistor. Accordingly, the base to emitter voltage of first transistor is higher than that of the second transistor and a delta VBE is generated at the base of the first transistor with respect to the base of the second transistor. A first voltage divider generates a divided voltage of a VBE (fractional VBE) at a first center node. The fractional VBE is added to the VBE of the first transistor and subtracted from the VBE of the second transistor by closed loop feedback action to generate a temperature compensated reference voltage at the base of second transistor. The reference voltage can be amplified to higher voltage levels by using a resistor divider at the base of second transistor.